COORDINATED MEASUREMENTS OF AURORAL LIGHT INTENSITIES AND RIOMETRIC RADIOWAVE ABSORPTION

Digitized allsky images of auroral optical emissions, recorded by a lo w light level TV system at Sanae (70.3 degrees S, 2.40 W, L = 4.0), ha ve been mapped onto the angular sensitivity functions of both a broad, single-beam riometer and narrow beams of an imaging riometer. During the rising phase of a substorm before local magnetic midnight, on 11 M ay, 1992, the integrated optical intensities in the inner four beam di rections of the 16-beam imaging riometer followed each other fairly cl osely, while the absorptions showed marked spatially inhomogeneous dis tributions. Regions of ionospheric: absorption appeared not to coincid e spatially with regions of discrete optical structures, brit were adj acent to these structures. A small step of similar to 0.09 dB in absor ption was observed shortly after onset of the substorm on 27 July, 197 9, and again on 11 May, 1992, but before the sharp increase in absorpt ion. This step in absorption may be due to highly enhanced E-region el ectron temperatures arising from strong de electric fields connected t o auroral arcs. During the event of 9 June, 1991, which started with a n SSC at 00:40 UT, enhancements in absorptions followed enhancements i n optical emissions repeatedly after 52 s.